Excitation energy dependence of photoinduced absorption in intrinsic a-Si:H

We have studied subgap absorption of intrinsic a-Si:H induced by below- and above-gap photoexcitation. We find very similar photoinduced subgap absorption spectra when excited with 2.4 eV or 1.2 eV light. Both spectra exhibit a power-law dependence on laser intensity ?T ~ 1a, where a is 0.5 and 0.7 for 2.4 and 1.2 eV excitation energy, respectively. This behavior indicates a change in the recombination mechanism as a function of excitation energy. The PA spectrum excited at 1.2 eV shows a strong dependence on bias illumination. Bias illumination bleaches the absorption according to a power-law as ?T = c(Ebias)-I(1, where P is approximately 0.85 and independent of probe energy and bias energy. The parameter c(Ebias) increases superlinearly with bias illumination energy for Ebias > 1.7 eV